The present invention relates to a heat-sealable laminating film with lamination and heat-sealable sides, and having excellent antifogging properties at low temperatures. The film according to the present invention, in conjunction with a suitable supporting film, is suitable in particular for packaging moist, oxygen-sensitive products such as fresh meat for example, which are presented chilled to the purchaser. In such an instance, suitable packaging, using the laminating film according to the invention ensures optical package properties which are not disturbed by condensation on the inside. The present invention also relates to composites which include the heat-sealable laminating film according to the invention as one component together with use of the heat-sealable laminating film or the packaging materials containing said film for packaging foodstuffs.
Fresh meat products are increasingly offered to the consumer in ready-to-use portions. In this way, better hygiene is ensured than is the case when the meat is cut into portions and packed by hand at a conventional meat counter in a supermarket, for instance. In addition, meat products which are previously cut into portions exhibit a longer shelf life than meat products cut to the customer""s individual requirements, owing to the more sterile cutting conditions and secure packaging.
This market development brings with it particular requirements with regard to the films used for packaging such pre-portioned meat products. Thus, in most cases the packaging used is lidded packaging consisting of a rigid tray and a transparent lid. Both components have to have good oxygen barrier properties to protect the product from oxidative deterioration. In addition, the lid film has to exhibit good transparency, in order to allow the consumer to see the product on offer and to be able to present it as attractively as possible. As a result of chilled storage and the moisture-saturated atmosphere in the packaging, condensation typically arises on the inside of the transparent lid. This condensation is disturbing in that it leads to fogging of the lid film and thus an impaired view of the product. Since the deposition of moisture contained in the package on the surface of the packaging cannot in principle be prevented, lid films are required which allow condensation in the form of a continuous liquid film, which thus does not impair transparency.
Laminated lidding films with a stretched supporting film and a heat-sealable layer of polyethylene or ethylene copolymers have been widely used for a relatively long period.
The need for a stretched supporting film stems primarily from the improved machine processing characteristics of such composites, owing to the high rigidity thereof, in comparison with unstretched films. Biaxially oriented polypropylene (BOPP) or biaxially oriented polyethylene terephthalate (BOPET) are predominantly used as supporting films. The corresponding types do not have the oxygen barrier properties necessary for the above-described use without further finishing, such as for instance oxide vapor deposition.
Where the supporting film itself does not have adequate oxygen barrier properties, the heat-sealable layer generally comprises multilayer films of polyethylene and/or ethylene copolymers, which have one or more layer(s) of ethylene/vinyl alcohol copolymers (EVOH) as an oxygen barrier. These films are designated hereinafter as xe2x80x9cheat-sealable barrier layerxe2x80x9d or xe2x80x9cheat-sealable barrier layer films.xe2x80x9d The structure of such heat-sealable barrier layer films is described, for example, in EP-A 560 495, EP-A 561 428, U.S. Pat. No. 4,726,984 and U.S. Pat. No. 4,547,433.
The low surface tension of polyethylene or ethylene copolymers on the heat-sealable side of the stated multilayer oxygen-blocking heat-sealable layers does not allow a substantial amount of wetting on contact with water but rather leads to the formation of water droplets on the surface. In a sufficiently finely dispersed form, which is achieved on the surface for instance during a condensation process, these droplets lead to marked haziness of the film. This phenomenon is conventionally known as fogging.
In this regard, the use of migrating additives in heat-sealable barrier layers is known to achieve wettability with water. Esters of polyhydric alcohols such as sorbitan or glycerol with saturated or unsaturated aliphatic carboxylic acids, generally containing between 8 and 40 carbon atoms, are generally used as the additive. Mono- and/or diesters are preferably used. Another class of additive conventionally used consists of polyoxyethylene compounds. Ethers of polyoxyethylene with higher aliphatic alcohols are typically used, for example, in this regard.
A product which is totally satisfactory for this application from the point of view of both concentration and composition of the additives and also the structure of the heat-sealable barrier layer has not yet been found. Indeed, the large number of patent applications in this field, such as for example EP-A 739 398, shows that a considerable need has yet to be met.
A particular requirement placed on heat-sealable barrier layers having antifog properties is the desire for the antifogging action to begin soon after the packaging process and to last for a sufficiently long time.
In addition, in order for the film to run in a problem-free manner through the packaging machine it must exhibit good surface slip properties in particular with regard to metal. This is typically not the case with films with antifog properties, since the migrating antifog agent is deposited on the surface and forms a layer thereon which is matt and tacky owing to its chemical composition.
In practice, heat-sealable barrier layers with antifog properties are frequently also observed to exhibit a slight delamination tendency. This effect is a consequence of the reaction during coextrusion of the acid groups contained in coupling agents with the non-esterified hydroxyl groups of the polyhydric alcohols of the antifog agents used. As a consequence, a further requirement is for the layers of the composite to be as difficult to separate as possible.
Thus, an object of the present invention is to provide a heat-sealable barrier layer having an antifog action beginning soon after packaging and lasting a sufficiently long time, good surface slip with regard to metal, and high mechanical integrity.
In accordance with the present invention, there is provided a multilayer film having a lamination side and a heat-sealable side comprising:
a) an inner layer (i) of comprising ethylene/vinyl alcohol copolymer;
b) a coupling agent layer (ii) and a separate coupling agent layer (iixe2x80x2), said inner layer (i) being interposed between and in contact with each of said coupling agent layer (ii) and said separate coupling agent layer (iixe2x80x2);
c) at least one further layer (iii), said separate coupling agent layer (iixe2x80x2) being interposed between and in contact with each of said inner layer (i) and said layer (iii);
d) at least one layer (iv), said coupling agent layer (ii) being interposed between and in contact with each of said inner layer (i) and said layer (iv); and
e) a heat-sealable layer (v), said layer (iv) being interposed between and in contact with each of said coupling agent layer (ii) and said heat-sealable layer (v);
wherein said multilayer film contains sorbitan monoester in an amount totaling from 0.1 to 3 wt. % based on the total weight of said multilayer film, said layer (iii) defining said lamination side of said multilayer film, and said heat-sealable layer (v) defining said heat-sealable side of said multilayer film. In an embodiment of the present invention, the multilayer film contains 0.3 to 1 wt. % of the sorbitan monoester, based on the total weight of the multilayer film.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified in all instances by the term xe2x80x9cabout.xe2x80x9d
Unless otherwise noted, the following conventions are applicable to the multilayer films described herein.
Where not otherwise stated, abbreviations for plastics in accordance with DIN 7728 or ISO 1043-1987 (E) are used in the description of the polymers contained in the individual layers.
In multilayer structures, the sequence of layers is stated by stringing together the polymer abbreviations for the corresponding layers or otherwise explained symbols, separated from each other by double oblique slashes. The heat-sealable layer side is always on the right. It is also possible to state only part of the total sequence of layers constituting the film. In these cases, the heat-sealable layer side is again always on the right and unstated layers or combinations of layers are indicated by three full stops (i.e., . . . ). Similar polymers may be distinguished from one another by numbering, for example as in PE-LD-1//PE-LD-2//PE-LD-3. Mixtures of different polymers are indicated by the symbol+and the combination of components between parenthesis, ( ). Details of percentage composition may optionally also be stated here. Unless otherwise stated, the fractions stated are always fractions by weight relative to the total weight of the mixture. The expression . . . //PA//E/VOH// . . . //(PE-LD-1+PE-LLD)//d, for example, thus describes a structure having an unspecified outer layer or outer sequence of layers, followed by a layer substantially consisting of polyamide, followed by a layer substantially consisting of ethylene/vinyl alcohol copolymer (E/VOH), followed by an unspecified layer or sequence of layers, followed by a layer comprising a mixture of low density polyethylene provided with the number 1 (PE-LD-1) and an ethylene/-olefin copolymer (PE-LLD), together with a following layer on the heat-sealable side to be specified in greater detail with d.
Layers which primarily provide a mechanical bond between the layers adjoining them on both sides are designated below as . . . //HV// . . . , wherein HV serves an abbreviation for coupling agent. Typical polymers used as coupling agents are described below.
Melting points are stated hereinafter with reference to the value determined in accordance with ASTM 3418 using DSC analysis (Differential Scanning Calorimetry Analysis).
Softening points are stated hereinafter with reference to the value determined in accordance with ISO 306.
Melt flow rates (MFR) are stated hereinafter with reference to the value determined in accordance with DIN ISO 1133. Unless stated otherwise, the measurement condition with regard to temperature and application weight is condition D of DIN ISO 1133, with a temperature of 190xc2x0 C. and an application weight of 2.16 kg.
The density of the raw materials relates to the measuring method according to ISO 1183 (A).